The nissan seats come apart quite easily so imo a "rebuild" of the seat would be easy I woukd think..
As long as the strapping under it is in good order.
But is it the base?
And what will help?
I am looking at doing my seats as let's be honest, the stock seats are shoit..
The seats in the Getz were like milk crates so better than them but still not brilliant.
I'm thinking of going mostly dense foam to give good support but then throw 40mm of memory foam on top, then the wings of the high density stuff again to retain shape..
I'm hoping it'll give good support but still allow me to sink into the seat a little..
Know idea on cost lol, just thoughts.

But everyone has there own opinion on what's comfortable so I recommend getting to a foam supplier and trying a couple of different layers and planting the hinie on em to get a feel that's right for you..